In industrial pressure measuring technology, pressure transfer means filled with a pressure transfer liquid are used for hydraulic transfer of pressures. These comprise regularly an isolating diaphragm outwardly sealing a pressure chamber and contactable externally with a pressure to be transmitted, and a pressure transfer path connecting the pressure chamber with a targeted location.
Pressure transfer means are applied in pressure measuring technology, e.g. in pressure measuring transducers, which comprise, arranged in a pressure measuring, chamber, a pressure sensor, which is supplied via the pressure transfer path with the pressure acting on the isolating diaphragm. In such case, these pressure transfer means serve for protecting the pressure sensor against direct contact with a medium, whose pressure is to be measured. Moreover, they serve for protecting the pressure sensor and electronic components connected therewith against high temperatures acting, in given cases, on the isolating diaphragm, temperatures which such components cannot regularly withstand.
Isolating diaphragms are, as a rule, circular or have a wave profile with waves arranged concentrically with the center of the diaphragm. These isolating diaphragms have a stiffness rising strongly non-linearly with increasing deflection of the isolating diaphragm from its middle position. The stiffer an isolating diaphragm is, the more strongly it corrupts a pressure to be transmitted through it.
For solving this problem, German Patent, DE 10 2005 023 021 A1 describes pressure transfer means with an isolating diaphragm formed as a wave diaphragm. Such isolating diaphragms have at least two different energetically favorable and therewith stable, rest positions. These pressures transfer means are filled with a predetermined amount of pressure transfer liquid, which is sized in such a manner that the isolating diaphragm is located during operation in a working position located between two neighboring rest positions. The means, however, that the isolating diaphragm is bistable and even small deflections of the isolating diaphragm lead to its wanting to go to the neighboring rest position.
There are applications, in which isolating diaphragms of pressure transfer means are exposed to high temperatures, especially temperatures above 200° C. At such temperatures, the pressure transfer liquid in the hydraulic path can evaporate or outgas. Especially problematic, in such case, are situations, in which a small pressure, especially an absolute pressure of less than 100 mbar, is to be transmitted via the isolating diaphragm. The evaporation occurs in the most favorable case reversibly according to the vapor pressure curve for the particular pressure transfer liquid. This can lead, especially in the case of small pressure to be transmitted, to considerable pressure measurement errors, and, in the worst case, even to a plastic deformation of the isolating diaphragm. Moreover, there is the danger that irreversible processes occur, in the case of which due to reactions with impurities or with the hydraulic path bounding surfaces, decomposition products form, which, after the outgassing, no longer return into solution.
For solving this problem, German Patent, DE 10 2004 052 950 A1 describes a pressure measuring transducer, which has a sensor module and a pressure transfer module placed in front of the sensor module.
The pressure transfer module includes                an isolating diaphragm outwardly sealing a first pressure chamber and externally contactable with a pressure to be transmitted,        a transfer diaphragm outwardly sealing a second pressure chamber, and        a pressure transfer path connecting the first pressure chamber with the second pressure chamber, wherein        the first and the second pressure chambers and the pressure transfer path are filled with a pressure transfer liquid, via which a pressure acting externally on the isolating diaphragm is transmitted to the transfer diaphragm.        
The sensor module connected with the transfer module includes                a receiving body,        in which a pressure receiving chamber is enclosed, and        which is connected pressure-tightly with the pressure transfer module in such a manner that the transfer diaphragm of the pressure transfer module outwardly seals the pressure receiving chamber,        a pressure sensor arranged in a pressure measuring chamber, and        a pressure transfer path connecting the pressure receiving chamber with the pressure measuring chamber, wherein        the pressure receiving chamber, the pressure measuring chamber and the pressure transfer path are filled with a second pressure transfer liquid, via which a pressure transmitted via the transfer diaphragm into the pressure receiving chamber is transmitted to the pressure sensor.        
This solution offers the advantage that the transfer module can be filled with its pressure transfer liquid isolated from the sensor module, wherein the filling of the transfer module occurs according to DE 10 2004 052 950 A1 preferably at a filling temperature, which lies above a maximum use temperature, to which the isolating diaphragm can be exposed during operation. In such case, the filling according to DE 10 2004 052 950 A1 occurs preferably at an as low as possible filling pressure, which according to an especially preferred form of embodiment amounts to no more than 25 mbar. In this way, it is possible to use the transfer module at significantly higher temperatures than is the case for a pressure transfer means connected via its hydraulic path directly with the pressure measuring chamber containing the pressure sensor. Also in this case, however, the maximum use temperature for the isolating diaphragm is upwardly limited.